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Session 1 - Solar magnetic variability and irradiance over the solar cycle

Conveners: Marc DeRosa (LMSAL), Jesper Schou (MPS)

The solar dynamo: Inferences from observations	Cameron, R
Robert Cameron [1]
Max Planck Instute for Solar System Research
We will show that the observed large-scale structure of the poloidal and toroidal magnetic fields, together with the differential rotation and surface meridional flow argue strongly in favour of a Babcock-Leighton dynamo. The cycle-to-cycle variability is consistent with the idea that flux emergence takes place in a turbulent environment, and we will discuss some of the implications of this in the context of the model.
Delayed Babcock-Leighton dynamos with high diffusion.	Fournier, Y
Yori Fournier[1], Rainer Arlt[1], Detlef Elstner[1]
[1]Leibniz Institute for Astrophysics Potsdam (AIP)
The solar dynamo is often attributed to the Babcock-Leighton mechanism in which magnetic flux tubes rise to the surface, turn into poloidal flux loops and eventually contribute to the global poloidal field of the Sun. The rise of the tubes is typically considered instantaneous, and the magnetic flux density at which the mechanism saturates is taken to be a value in equipartition with the convective motions. Such models deliver solar-like solutions only in the advective-dominated regime, requiring magnetic diffusivities significantly lower than the estimates. In this talk, we present delayed Babcock-Leighton dynamos employing rise times and saturation fields obtained from direct numerical simulations of rising magnetic flux tubes. We demonstrate that the non-linear effect due to the temporal non-locality (the delay) leads to exotic solutions which deliver solar-like activity in the diffusive-dominated regime.
Study of Ionosphere Variability over equatorial latitude during extreme low solar activity period	Purohit, D
P. K. Purohit & Roshni Atulkar
National Institute of Technical Teachers' Training and Research, Bhopal – 462002, MP, India.
The most important ionospheric parameter total electron content (TEC), derived by analyzing dual frequency signals from the Global Positioning System (GPS) recorded near the Indian equatorial anomaly region, Bengaluru (13.020 N, 77.570E) located within 0 - 15oN of the equatorial anomaly region. We studied Diurnal, monthly, seasonal and annual variability as well as geomagnetic and solar effects on the equatorial ionospheric anomaly (EIA) during the solar minimum period from January 2009 to December 2009. The monthly highest values of TEC are recorded during the March, April and October While the minimum TEC is observed during the month of June, July, December and January. Similarly, It is found that the daily maximum TEC near equatorial anomaly crest yield their maximum values for the period of the equinox months and their minimum values during the summer. Using monthly averaged peak magnitude of TEC, a clear semi-annual variation is seen with two maxima occurring in both spring and autumn. Relative standard deviation for VTEC shows high value at around morning and before sunrise. From the comparison of GPS-TEC with different solar indices, i.e. solar EUV flux(26–34 nm and0.1–50 nm), F10.7 cm solar radio flux and Zurich sunspot number (SSN), it is concluded that the solar index EUV flux is a better controller of GPS-TEC, compared to F10.7 cm and SSN. Keywords: - Total electron contents (TECs); Equatorial ionization anomaly (EIA); Global Positioning System (GPS)
The Sunspot Number recalibration	Lefevre, L
Laure Lefevre[1], Frederic Clette[1], Sophie Mathieu[1,2], Veronique Delouille[1], Rainer von Sachs[2]
[1]Royal Observatory of Belgium,[2]Institut de statistique, biostatistique et sciences actuarielles (ISBA), UCL
We will present here the revision of the Sunspot Numbers undertaken by the whole solar community since 2010 that led to the publication of a new series in 2015 (http://www.sidc.be/silso/newdataset). This well-known index of solar activity had not been revised since its creation by Rudolf Wolf in 1849. For the Sunspot Number, the k scaling coefficients of individual observers were recomputed using new statistical methodologies while the last 50 years were fully recomputed, using all original data from the 270 stations archived by the World Data Center - SILSO in Brussels. For the Sunspot Group Numbers, most corrections rely entirely on original sunspot data, using various approaches. Newly recovered historical sunspot records were added and a critical data selection was applied for the 17th and 18th century, confirming the low solar activity during the Maunder Minimum. The new Sunspot Number series definitely exclude a progressive rise in average solar activity between the Maunder Minimum and an exceptional Grand Maximum in the late 20th century. Residual differences between the Group and Sunspot Numbers over the past 250 years confirm that they reflect different properties of the solar cycle. We also present preliminary results obtained in the context of the VALUSUN (BELSPO-BRAIN) project concerning the statistical modelling of the Sunspot Numbers: this includes constant quality control of the most recent part of the series and the inclusion of significant error bars. We conclude on the implications for solar cycle and Earth climate studies and on important new conventions adopted for the new series: new unit scales, new SN and GN symbols and a new version-tracking scheme implemented at the WDC-SILSO, as a framework open to future improvements of those unique data series.
Measurements of Solar Oblateness during the SDO Mission	Bush, R
R.I. Bush [1], M. Emilio [2], I. Scholl [3], J.R. Kuhn [3], J. Sommers [1]
[1] Stanford University, Stanford, CA, USA [2] Universidade Estadual de Ponta Grossa, Parana, Brazil [3] University of Hawaii, Hilo, HI, USA
Beginning in April 2010, the Helioseismic and Magnetic Imager (HMI) instrument on the Solar Dynamics Observatory (SDO) spacecraft has been making periodic measurements of the solar shape. The primary observations are 4096 by 4096 pixel full Sun images taken in the continuum of the 617.3 nm Fe I absorption line in 4 linear polarizations. It is necessary to determine the instrument optical distortion in order to extract the solar shape from the full Sun images. This is accomplished during a roll maneuver of the SDO spacecraft in which the spacecraft is rotated 360 degrees around the Sun-spacecraft line while taking a series of images at 32 uniformly spaced roll angles. Measurements of the solar oblateness are typically obtained twice per year, and eighteen roll maneuvers have been performed by the SDO spacecraft to date. Initially these observations were taken in April and October from 2011 to 2014. During the April 2015 roll, however, the spacecraft maneuver was aborted due to a pointing anomaly. This error condition was identified, but subsequent roll maneuvers were shifted to January and July of the following years. The mean equator to pole radius difference over the nine years of observations is 6.0 +/- 1.0 milli-arcseconds. The higher order (hexadecapole) term is consistent with 0. The long term trend of the solar oblateness does not show a correlation with the current solar sunspot cycle. Details of the measurements and trending will be discussed.
Soothing Massage of HMI Magnetic Field Data	Hoeksema, T
J. Todd Hoeksema[1], Yang Liu[1], Xudong Sun[2], Philip Scherrer[1] & the HMI Science Team
[1]Hansen Experimental Physics Laboratory, Stanford University; [2] Institute for Astronomy, University of Hawai'i at Manoa
The Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) has measured solar polarization at six wavelengths across the Fe I 6173 spectral line with one arc second resolution nearly every 90 or 135 seconds since May 2010, and the Stokes parameters are determined every 720 seconds over the full disk. The quality of the filtergrams is remarkably uniform, but the inverted and disambiguated magnetic field values are sometime incorrect or show small systematic variations with time and space. Estimates of the numerical uncertainties are provided for each pixel, but, for some kinds of analysis, having a smoother and more uniform time series can be useful. This report describes methods that can be used to 'massage' the observations to improve consistency and appearance and minimize unwanted variability. Effects considered include issues related to field inversion, disambiguation, instrument sensitivity, optical distortion, and systematic errors due to spacecraft velocity. The resulting 'corrections' typically depend on assumptions about the behavior of the solar magnetic field, so care must be taken when using such results.
On the acoustic mode frequency dependence with solar cycle	Rabello soares, M
M. Cristina Rabello-Soares
Universidade Federal de Minas Gerais
Global modes obtained by applying spherical harmonic decomposition to HMI, MDI and GONG full-disk observations were used. The dependence of solar acoustic mode frequency with solar activity was examined and evidence of a deviation from a linear relation was found indicating a saturation effect at high solar activity. The frequency dependence of frequency differences between the activity minimum and maximum was analyzed.
Tracking of predominant periodicities evolution for PROBA2/LYRA and other long-term solar time series	Wauters, L
Laurence Wauters[1], Marie Dominique[1],Ingolf Dammash[1],Mustapha Meftah
[1]Royal Observatory of Belgium, [2]LATMOS / CNRS / Paris-Saclay University
The periodograms of the PROBA2/LYRA data show predominant periodicities comparable to the ones observed by other solar time series for the same time range. These periodicities have been found to slightly vary over time. Tracking their evolution on a long-term basis aims at identifying which periodicities are related to each other and at determining which physical processes are at their origin. A study has been made on sunspot area, for which several solar cycles of data exist and for which the periodicities are close to the ones found in LYRA (for the same time range). We used framed Lomb-Scargle periodograms to extract the periodicities and check their evolution. Several significant periodicities behave similarly and seem to be harmonically related.
The photospheric structure of coronal holes: magnetic elements	Hofmeister, S
Stefan Hofmeister, Dominik Utz, Stephan Heinemann, Astrid Veronig, Manuela Temmer
Institute of Physics, University of Graz, Graz, Austria
Coronal holes attracted recently more attention by the scientific community as they represent the source region for the fast solar wind which is ifself an important ingredient in understanding the space environment and space weather. Nevertheless, our knowledge about the detailed magnetic field structure below coronal holes is quite limited, maybe since such a research would necessarily involve the high atmospheric and photospheric community. In this contribution we would like to bridge this gap and investigate in detail the magnetic field distribution below coronal holes and its relationship to the large-scale coronal hole topology. To do so, we investigate the distribution and properties of photospheric magnetic elements below 106 low and medium latitude coronal holes using SDO/HMI line-of-sight magnetogram data from 2010 to 2016, and relate them to the overall properties of the coronal holes. Since magnetic elements produce clearly visible photospheric structures, they can be well observed and give us valuable insights into the structure of coronal holes. We find that the distribution of the magnetic flux of magnetic elements follows an exponential function. The area and flux of magnetic elements are strongly related to each other by a power law with an exponent of 1.25. The larger magnetic elements are located at the edges of the magnetic network and seem to be the “core” structure of coronal holes. They have lifetimes > 4 days, i.e., longer than the timescale of the supergranulation. Further, they contain up to 50 magnetic bright points as observed by Hinode/SOT in the G-Band, meaning that the large magnetic elements are large clusters of individual magnetic elements. The mean magnetic field density of the overall coronal holes and thus their unbalanced magnetic flux is determined by their percentage coverage with magnetic elements at cc=0.98. Since magnetic elements are the foot points of magnetic funnels and thus the small-scale source regions of high-speed solar wind streams, the dependence of the coverage with magnetic elements on the strength of coronal holes also explains the dependence of the plasma density of high-speed streams near the Sun to the strength of its source coronal hole. The rotation rates of the magnetic elements match the rotation rate of the coronal hole and is surprisingly similar to the differential rotation rate of active regions at low- and medium latitudes, suggesting they are rooted at similar deep layers. This also means that coronal holes do not show an abnormal rotation rate as suggested by various authors. Finally, by projecting the magnetic elements to AIA-171 and 193 filtergrams, we surprisingly find that the magnetic elements are not located in the darkest regions of coronal holes. Therefore, the vertical plasma outflow from magnetic funnels is probably not the primary reason why coronal holes appear as dark patches in EUV images. We conclude that magnetic elements are the basic building blocks of coronal holes which completely determine their magnetic properties.

Session 2 - Precursors and signatures of eruptive events

Conveners: Barbara Thompson (GSFC), James Mason (GSFC)

Spatiotemporal Heliomarker Discovery from Spatiotemporal Frequent Patterns	Aydin, B
Berkay Aydin, Rafal Angryk
Georgia State University
Heliomarkers, short for “heliophysical markers”, are the indicators or signs of important solar phenomena, whose aim is to objectively identify the current state of the sun or indicate a future state of it. Two specific aims of discovering heliomarkers are understanding the characteristics of solar events and predicting the incidence of important solar events. The desired properties of heliomarkers can be summarized as: (1) Validity (accurate, specific, sensitive, and precise), (2) Robust (handles noisy data or data with missing values) (3) Reproducible (over different datasets from different observatories and time spans) and (4) Interpretable. We will present our efforts on discovering spatiotemporal heliomarkers using spatiotemporal frequent patterns. The spatiotemporal frequent patterns are the frequently repeating relationships occurring among the solar events. These include spatiotemporal co-occurrences or event sequences. We conducted our analyses using the tracked and interpolated solar event data. The solar event data represents the spatial vector metadata detected from SDO imagery. We will present the current state of our research and the discovered heliomarkers.
A study on the relationship between hard X-ray emission and magnetic field changes during solar flares	Caicedo, W
[1] Willinton Caicedo Tez, [2]Juan Sebastian Castellanos, [3]Benjamín Calvo Mozo
[1]Universidad Nacional de Colombia,[2] Max Planck Institute for Solar System Research,[3]Universidad Nacional de Colombia
During solar flares it has been observed that the photospheric magnetic field changes significantly, abruptly and permanently. We investigated the possible spatial and temporal correlation between permanent magnetic field changes during 6 solar flares. These highly energetic events occurred during the current solar cycle 24. The energy range of the flares contains events from low energetic to very energetic, according to the GOES classification. The behavior of the emission of hard X-rays (HXR) and the magnetic fields is analyzed using data from the RHESSI and SDO/HMI satellites. We study the probability that the photospheric magnetic field will change due to the particle injection in the lower layers of the solar atmosphere. At present there is no statistical study that relates these processes during flares.
Detection of Three-minute Oscillations in Full-disk Lyman-alpha Emission during a Solar Flare	Milligan, R
Ryan O. Milligan[1], Bernhard Fleck[2], Jack Ireland[3], Lyndsay Fletcher[1], Brian R. Dennis[4]
[1]University of Glasgow, [2]ESA Directorate of Science, c/o NASA/GSFC, [3]ADNET Systems, Inc., [4]NASA/GSFC
In a recent study of spatially-integrated Lyman-alpha line emission (Lya, 1216A) from GOES/EUVS, we detected the presence of acoustic 3-minute oscillations during an X-class solar flare. Similar periodicities were also found - in phase - in Lyman continuum data from SDO/EVE, and the 1600A and 1700A channels on SDO/AIA. The implication is that the chromosphere responds dynamically at its acoustic cutoff frequency to an impulsive injection of energy. Since the 3-minute period was not detected at hard X-ray energies in RHESSI data we can state that this 3-minute oscillation does not depend on the rate of energisation of non-thermal electrons. This finding suggests that chromospheric mechanical energy should be included in the flare energy budget, and that fluctuations in Lya emission may influence the composition and dynamics of planetary atmospheres during periods of high activity. Knowledge of the behaviour of this emission during flares could be important when interpreting future science results from the EUI instrument on Solar Orbiter which will obtain high cadence images in Lya.
Multi-wavelength observations of 4 homologous global coronal waves	Long, D
David Long[1], Julia Lawless[2], Gherardo Valori[1], Jack Jenkins[1]
[1] Mullard Space Science Laboratory, University College London; [2] Trinity College Dublin
Global coronal waves (commonly called “EIT waves”) were first observed by SOHO/EIT in 1997 and are now considered to be large-scale shock fronts initially driven by the rapid expansion of an erupting coronal mass ejection in the low corona. I will present observations of four homologous global waves which erupted from the same active region over the course of three days in March 2014. Each global EUV wave was well observed by SDO/AIA and was associated with a H-alpha Moreton-Ramsey wave observed at high cadence by the GONG network. These observations provide the opportunity to directly relate global waves in EUV and H-alpha observations with high cadence and answer a fundamental question about the relationship between these phenomena which has persisted since they were first observed.
AWARE: An algorithm for the automated characterization of EUV waves in the solar atmosphere	Ireland, J
Jack Ireland[1], Andrew Inglis[2], Albert Shih[3], Steven Christe[3], Stuart Mumford[4], Laura Hayes[5], Barbara Thompson[3], Keith Hughitt[6]
[1] ADNET Systems, Inc., MD, USA, [2] Catholic University, DC, USA, [3] NASA GSFC, MD, USA, [4] University of Sheffield, UK, [5] Trinity College Dublin, ireland [6], NIH, MD, USA
Extreme ultraviolet (EUV) waves are large-scale propagating disturbances observed in the solar corona, frequently associated with coronal mass ejections and flares. They appear as faint, extended structures propagating from a source region across the structured solar corona. Since their discovery, over two hundred papers discussing their properties, causes and physical nature have been published. However, despite this their fundamental properties and the physics of their interactions with other solar phenomena are still not understood. To further the understanding of EUV waves, we have constructed the Automated Wave Analysis and REduction (AWARE) algorithm for the measurement of EUV waves. AWARE is implemented in two stages. In the first stage, we use a new type of running difference image, the running difference persistence image, which enables the efficient isolation of propagating, brightening wavefronts as they propagate across the corona. In the second stage, AWARE detects the presence of a wavefront, and measures the distance, velocity and acceleration of that wavefront across the Sun. The fit of propagation models to the wave progress isolated in the first stage is achieved using the Random Sample and Consensus (RANSAC) algorithm. AWARE is tested against simulations of EUV wave propagation, and is applied to measure EUV waves in observational data from the Atmospheric Imaging Assembly (AIA). We also comment on unavoidable systematic errors that bias the estimation of wavefront velocity and acceleration. In addition, the full AWARE software suite comes with a package that creates simulations of waves propagating across the disk from arbitrary starting points.
Understanding the Role of Mass-Unloading in a Filament Eruption	Long, D
Jack Jenkins[1], David Long[1], Lidia van Driel-Gesztelyi[1,2,3], Jack Carlyle[4], Matthew Hopwood[5,6]
[1] Mullard Space Science Laboratory, University College London; [2] Observatoire de Paris; [3] Konkoly Observatory; [4] ESAC; [5] School of Mathematics, University of Birmingham; [6] School of Mathematical Science, University of Adelaide
We combine observations of a partial filament eruption on 11 December 2011 with a simple line-current model to demonstrate that including mass is an important next step for understanding solar eruptions. Observations from the Solar Terrestrial Relations Observatory-Behind (STEREO-B) and the Solar Dynamics Observatory (SDO) spacecraft were used to remove line-of-sight projection effects in filament motion and correlate the effect of plasma dynamics with the evolution of the filament height. The two viewpoints enable the amount of mass drained to be estimated, and an investigation of the subsequent radial expansion and eruption of the filament. We use these observational measurements to constrain a line-current model and quantitatively demonstrate the important role that the presence and draining of mass has in the lead-up to solar eruptions. Specifically, we show that the balance of magnetic and gravitational forces acting on the line-current is increasingly sensitive to mass perturbations as it approaches its loss-of-equilibrium. Finally, we conclude that the eruption of the observed filament was restrained until 70% of the mass had drained from the structure.
Oscillations along Flare Loops in Multiple Wavelengths and their Correlations to Photospheric Waves	Hess webber, S
Shea A. Hess Webber[1], Junwei Zhao[1]
[1]Stanford University
The goal of this work is to determine whether oscillations along flare loops have a detectable response to/in the photosphere. Using multiple SDO/AIA wavelengths, we track plasma oscillations in the chromosphere and low corona before and after several M- and X-class flares. These results will be used to determine travel times for the oscillations along the flare loops. We correlate these travel times with photospheric wave responses. Understanding if and how flare oscillations interact with the photosphere can detail the mechanics and solar environment in flaring active regions.
Dynamic Mapping of Solar Eruptions	Thompson, B
Barbara J Thompson[1], C. Richard DeVore[1], Beryl A. C. Hovis-Afflerbach[1,2], Vadim Uritsky[3]
[1]NASA Goddard Space Flight Center, USA, [2]California Institute of Technology, [3]Catholic University of America
We present the results of a prominence mapping effort designed to extract the dynamics of erupting prominences and CMEs. The material from partially erupting prominences can fall back to the sun, tracing out the topology of the mid- and post-eruptive corona. One question involving the range of observed behavior is the role of magnetic field topology and evolution in determining the motion of the erupting prominence material. A variable-g ballistic approximation is applied to study the motion of the material, using the deviations from constant angular momentum as a means of quantifying the local Lorentz (and other) forces on each piece of material. Variations in dynamic behavior can be traced back to changes in the local magnetic field. We discuss the use of the prominence trajectories as a means of diagnosing eruptive topologies.
On the Magnetic Topology and Extreme Ultraviolet in Solar Flares with Late Phase	Chen, J
Jun Chen[1][2], Rui Liu[1], Kai Liu[1], Yuming Wang[1]
[1]University of Science and Technology of China, [2]University of Potsdam
It was recently discovered that some solar flares exhibit a late-phase peak in EUV emission with `warm' temperatures (e.g., Fe XVI 33.5 nm), which is referred to as EUV late phase. In this work, we carried out a statistical study of 51 M- and X-class flares with EUV late phase (ELP) during 2010--2015. These flares are categorized as circular-ribbon, two-ribbon, and intricate-ribbon flares, based on the flare morphology observed in the chromosphere. It is found that the circular-ribbon flares with ELP often possess a coronal null and the associated fan and spine, which are typically embedded in a dome-shaped quasi-separatrix layer (DQSL) intersecting with a curved plate-shaped QSL (PQSL). The footprints of the PQSL correspond to an extended ribbon enclosed by the circular-shaped ribbon and a remote ribbon. The coronal loops responsible for ELP are found to be closely associated with not only the spine but more generally the PQSL. The majority of two-ribbon flares with ELP are confined, and the two ribbons are not associated with any preexisting QSLs. It is still an open question whether the ELP is primarily due to plasma cooling or additional heating.
A Truly Global Extreme Ultraviolet Wave from the SOL2017-09-10 X8.2+ Solar Flare-Coronal Mass Ejection	Liu, W
Wei Liu [1,2,3], Meng Jin [1,4], Cooper Downs [5], Leon Ofman [6,7,8], Mark C. M. Cheung [1], Nariaki V. Nitta [1]
[1] LMSAL, [2] BAERI, [3] Stanford Univ., [4] SETI, [5] Predictive Science, Inc., [6] CUA, [7] NASA/GSFC, [8] Tel Aviv University
We report SDO/AIA observations of an extraordinary global extreme ultraviolet (EUV) wave triggered by the X8.2+ flare-CME eruption on 2017 September 10. This was one of the best EUV waves ever observed with modern instruments, yet it was likely the last one of such magnitudes of Solar Cycle 24 as the Sun heads toward the minimum. Its remarkable characteristics include the following. (1) The wave was observed, for the first time, to traverse the full-Sun corona over the entire visible solar disk and off-limb circumference, manifesting a truly global nature, owing to its exceptionally large amplitude, e.g., with EUV enhancements by up to 300% at 1.1 Rsun from the eruption. (2) This leads to strong transmissions (in addition to commonly observed reflections) in and out of both polar coronal holes, which are usually devoid of EUV waves. It has elevated wave speeds >2000 km/s within them, consistent with the expected higher fast-mode magnetosonic wave speeds. The coronal holes essentially serve as new "radiation centers" for the waves being refracted out of them, which then travel toward the equator and collide head-on, causing additional EUV enhancements. (3) The wave produces significant compressional heating to local plasma upon its impact, indicated by long-lasting EUV intensity changes and differential emission measure increases at higher temperatures (e.g., log T=6.2) accompanied by decreases at lower temperatures (e.g., log T=6.0). These characteristics signify the potential of such EUV waves for novel magnetic and thermal diagnostics of the solar corona on global scales.
Estimation of Halo CME’s radial speeds using coronal shock waves based on SDO/AIA observations	Jeong, H
Hyunjin Jeong and Yong-Jae Moon
School of Space Research, Kyung Hee University
We propose a method to estimate the radial speed of a Halo CME by combining a coronal shock front and an EUV-wave that occurs on the solar disk. According to recent studies, EUV-wave occurs as a footprint of the coronal shock wave on the lower solar atmosphere. In this study, the coronal shock on 2011 February 15 by SDO/AIA is assumed as a perfect sphere. This assumption makes it possible to determine the height of a coronal shock, by matching the position of an EUV-wave on the solar disk and a coronal shock front on the SOHO/LASCO coronagraph image. The radial velocity of the Halo-CME is calculated from the rate of coronal shock position shift. The calculated speed from this method is a little slower than the 3-D velocity estimated by multi-spacecraft, but much faster than the projected one by SOHO/LASCO. And these results and the efficiency of this approach are discussed.
Effect of transport coefficients on excitation of flare-induced standing slow-mode waves in coronal loops	Wang, T
Tongjiang Wang[1,2], Leon Ofman[1,2], Xudong Sun[3], Sami K. Solanki[4], and Joseph M. Davila[2]
[1]Catholic University of America, USA; [2]NASA Goddard Space Flight Center, USA; [3]University of Hawaii, USA; [4] Max-Planck-Institut for Solar System Research, Germany
We analyze and model a flare-induced longitudinal oscillation event detected by SDO/AIA. The magnetic field extrapolation and flare emission features suggest that the wave event is generated by slipping and null-point-type reconnections in a closed fan-spine magnetic topology, and the large spine loop appears to be heated impulsively to the flare temperature before the wave disturbances travel along it. By means of the seismology technique, we determine the transport coefficients in hot (about 10 MK) plasma, and find that thermal conductivity is strongly suppressed and compressive viscosity is enhanced by more than an order of magnitude from the observed wave properties. We investigate the standing slow-mode wave excitation mechanism using 1D nonlinear MHD simulations based on two types of loop models. Model 1 with the classical transport coefficients and Model 2 with the seismology-determined transport coefficients. We find that Model 2 can form the standing wave pattern (within about one period) from initial propagating disturbances much faster than Model 1, in better agreement with the observations. Simulations of harmonic waves and the Fourier decomposition analysis reveal a scaling between damping time (Td) and wave period (P) following Td ~ P^2 in Model 2, while Td ~ P in Model 1. This suggests that anomalously large viscosity can efficiently enhance the dissipation of higher harmonic components, favoring quick setup of the fundamental standing mode. Our study suggests that observational constraints on the transport coefficients are crucial in understanding both the wave excitation and damping mechanisms.

Session 3 - Subsurface motions and flows

Conveners: Dean Pesnell (GSFC), Rebecca Centeno (HAO/NCAR)

On the depth dependence of solar equatorial Rossby waves	Proxauf, B
Bastian Proxauf[1,2], Laurent Gizon[1,2] , Björn Löptien[1], Aaron C. Birch [1], Jesper Schou[1], Richard S. Bogart[3]
[1]Max Planck Institute for Solar System Research, [2]University of Göttingen, [3]W. W. Hansen Experimental Physics Laboratory, Stanford University, USA
Here we use local helioseismology and local correlation tracking of granulation to infer horizontal flows on the solar surface and in the interior. From these flows, we compute maps of the radial vorticity at different depths in order to study Rossby waves. We show that the frequencies of these waves agree well with a simple theoretical dispersion relation. Also, we show that Rossby waves have significant amplitudes in the first 20 Mm below the surface and investigate the dependence of the Rossby waves on depth. We find an unexpected, presumably spurious dip in the wave power and a depth-independent phase and we conclude that further studies are needed.
First comprehensive calculation of the whole solar convection zone	Hotta, H
H. Hotta [1], H. Iijima [2], K. Kusano [2]
[1] Chiba university, [2] Nagoya university
The solar convection zone is filled with the turbulent convection zone in highly stratified plasma. The temporal and spatial scales vary significantly in the solar convection zone due to large density and temperature contrasts. The temporal and spatial scales of the thermal convection at the bottom of the convection zone are a month and the 200 Mm, while those are minutes and 1 Mm at the solar surface, respectively. Due to these significant changes, the numerical calculations for the deep convection zone and the solar surface are almost completely separated and direct comparisons between the deep convection zone and the photospheric observation are limited. The thermal convection is excited at the efficient cooling at very thin cooling layer around the surface and descends to the deep convection zone. It is inevitable to cover whole convection zone in a comprehensive calculation in order to understand the thermal convection itself. We, for the first time, succeed in carrying out such a comprehensive calculation covering the whole convection zone. We implement the realistic radiative transfer around the surface and our new version of the equation of state is applicable both to the deep convection zone and the solar surface. We now have a way to compare the deep convection calculation and the photospheric observation directly using our new calculations. We find that the influence of the solar surface is unexpectedly weak on the deep convection. We report the detailed analysis and future application of our calculation.
Subsurface Flows During Cycle 23 and 24	Komm, R
Rudolf Komm[1], Rachel Howe[2], Frank Hill[1]
[1]National Solar Observatory, Boulder, CO 80303, [2]University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
We study the solar-cycle variation of subsurface flows from the surface to a depth of 16 Mm. We have used ring-diagram analysis to analyze Dopplergrams obtained with the MDI Dynamics Program, the GONG, and the SDO/HMI instrument. We combine the zonal and meridional flows from the three data sources and we derive their temporal variation in a consistent manner for Solar Cycle 23 and 24. For Cycle 24, the flow patterns are precursors of the magnetic activity. The timing difference between the occurrence of the flow pattern and the magnetic one increases almost linearly with increasing latitude. For example, the fast zonal and meridional flow appear about 2.1 years and 2.5 years respectively before the magnetic pattern at 30 degree latitude in the northern hemisphere, while in the southern one the differences are 3.2 years and 2.6 years. The flow patterns of Cycle 25 are present and have reached 30 degree latitude. The amplitude differences of Cycle 25 are about 22% smaller than those of Cycle 24 but comparable to those of Cycle 23. In addition, we divide the data into subsets of low and high magnetic activity and study the variation of the quiet- and active-region flows during Solar Cycle 23 and 24.
The HMI Ring-Diagram Pipeline: Recent Developments and Future Prospects	Bogart, R
Richard Bogart[1],Charles Baldner[1],Sarbani Basu[2],Kiran Jain[3],Shea Hess Webber[1]
[1]Stanford University,[2]Yale University,[3]National Solar Observatory
The HMI ring-diagram pipeline produces tracked Doppler data cubes at three different size and time scales, their power spectra, two independent types of "mode" (ridge) fits to the spectra, and inversions of fit parameters measuring the mean near- and sub-surface flows. Ancillary products include measures of the mean magnetic activity associated with the tracked cubes, rotation averages of the power spectra at different Stonyhurst locations, and long-term averages of the input Dopplergrams. Active efforts are currently underway to improve many of these products. We review recent changes to the analysis procedures and products, discuss known problems, and describe modifications and updates in progress, under development, and/or contemplated for the near future.
The Minimum Energy Principle Applied to Parker's Coronal Braiding and Nanoflaring Scenario	Aschwanden, M
Markus Aschwanden [1] and A.A. van Ballegooijen [2]
[1] Lockheed Martin, Solar and Astrophysics Laboratory, [2] Harvard-Smithonian Center for Astrophysics
Parker's coronal braiding and nanoflaring scenario predicts the development of tangential discontinuities and highly misaligned magnetic field lines, as a consequence of random buffeting of their footpoints due to the action of sub-photospheric convection. The increased stressing of magnetic field lines is thought to become unstable above some critical misalignment angle and to result into local magnetic reconnection events, which is generally referred to as Parker's ``nanoflaring scenario''. In this study we show that the minimum (magnetic) energy principle leads to a bifurcation of force-free field solutions for helical twist angles at |phi(t)| = pi, which prevents the build-up of arbitrary large free energies and misalignment angles. The minimum energy principle predicts that neighbored magnetic field lines are almost parallel (with misalignment angles of Delta mu ~ 1.6-1.8 deg, and do not reach a critical misalignment angle prone to nanoflaring. Consequently, no nanoflares are expected in the divergence-free and force-free parts of the solar corona, while they are more likely to occur in the chromosphere and transition region.
Interactions of waves with solar convection	Schou, J
Jesper Schou
Max-Planck-Institut für Sonnensystemforschung
Some of the most significant problems in our understanding of solar and stellar oscillations are believed to be related to their interaction with the near surface convection. One such problem is the center to limb effect seen in many helioseismic measurements. Another the so-called surface term. Here I will briefly describe these problems and some preliminary results of trying to address them using large scale hydrocode simulations.
Rossby waves in the solar convection zone measured by deep-focus time-distance helioseismology	Duvall, T
T.L. Duvall Jr.[1], A.C. Birch[1], Z.-C. Liang[1], and L. Gizon[1][2]
[1] Max Planck Institute for Solar System Research, [2] Institut für Astrophysik, Georg-August-Universität Göttingen
Recent work by Loeptien et al. has shown spectral signatures of equatorial Rossby waves in the solar photosphere (via correlation tracking of granulation) and in the outer 20 Mm of the convection zone (via helioseismic ring diagrams). This result is potentially extremely important for understanding convection zone dynamics and as such should be studied by all available techniques. To this end we have searched for these Rossby waves using deep-focus time-distance helioseismology in 8 years of HMI medium resolution (medium l) Dopplergrams. We also see the signatures of equatorial Rossby waves for focus depths of 0 Mm (photosphere) down to 70 Mm below the surface. At 105 Mm (mid convection zone) and 210 Mm (bottom of convection zone) no such signatures are seen, although whether this is a s/n issue is not determined. We will hopefully be able to determine the radial eigenfunctions of the Rossby waves from this type of measurement.
Towards improved multi-ridge fitting method for ring-diagram analysis	Nagashima, K
Kaori Nagashima[1], Aaron C. Birch[1], Jesper Schou[1], Bradley Hindman[2], Laurent Gizon[1,3]
[1] Max-Planck-Institut für Sonnensystemforschung, [2] University of Colorado Boulder, [3] Georg-August-Universität Göttingen
Ring-diagram analysis is one of the important methods of local helioseismology for probing subsurface flows. In ring-diagram analysis the Doppler shifts of oscillation mode frequencies due to flows are measured by fitting a model function to the local oscillation power spectra. Here we propose alteration of the multi-ridge fitting method developed by Greer et al. (2014). It is well known that the solar oscillation power is chi-square distributed (with two degrees of freedom), and the fitting in the existing multi-ridge fitting is done with the maximum likelihood method based on this probability distribution function. However, the power is in practice remapped from Cartesian to polar coordinates and/or smoothed in azimuth of the wavevector. The smoothed power is approximately normally distributed. We demonstrate that the probability distribution function of the logarithm of the normally-distributed power is approximated by a normal distribution with a variance that is independent of the expectation value of the power. Therefore, we alter the fitting method using the logarithm of the power with a least-square method. In this presentation we report the bias and noise levels in the updated fitting results as well as the crosstalk between the parameters using a Monte Carlo simulation of the power spectra.
Impact of observational duty cycle on the measurement of local helioseismic mode parameters	Tripathy, S
Sushanta Tripathy[1], Richard Bogart [2], Kiran Jain[1]
[1]National Solar Observatory, Boulder, Co 80303 USA, [2] Stanford University, Sanford, CA 94305, USA
The effect of data gaps on the power spectra and the mode parameters can be explored by imposing a simulated observing window function on a continuous time series of predefined length as is used in standard ring diagram analysis. Here, we investigate the effect of these gaps in HMI data on board SDO through a Monte Carlo analysis. It may be noted that in case of HMI observations, the data gaps occur primarily due to the eclipses and calibrations and thus the distribution can be characterized by a two-element quasi-periodic population. From the Monte Carlo simulations, we examine (i) the presence or absence of the individual modes in the different fitting methods, (ii) systematic effects in frequencies and flow parameters, (iii) systematic effects in the inversions, and (iv) the extent to which these effects depend on the length of the analysis interval. As a base line, we use the absolutely continuous HMI data (no gaps) that are available for periods of up to a week but no more due to the weekly calibration of HMI and/or AIA data. The study uses data both from quiet and active periods.
A New Approach for Calculating Three-Dimensional Flow Sensitivity Kernels Using Global-Scale Wavefield Simulations	Zhao, J
Thomas Hartlep[1] & Junwei Zhao[2]
[1] Bay Area Environmental Research Institute, Moffett Field, California 94035, U.S.A. [2] W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, U.S.A.
At present, a common method for inferring the Sun's interior meridional-circulation profile is to invert helioseismically measured travel-time shifts using so-called sensitivity kernels describing the sensitivity of the travel times to flows in the interior. Ray-approximation kernels, despite their shortcomings, have been used by many authors and provided tremendous insight into the solar interior. In the meantime, more realistic global-scale Born-approximation kernels have been developed by some authors. Here, we introduce another approach for calculating three-dimensional flow kernels. In this approach, we perform global-Sun wavefield simulations with small flow perturbations placed at some location inside the simulated Sun and measure the travel-time shifts they cause. A linear equations links the flow model, we prescribe, and the travel-time shifts, we measure, with the sensitivity kernel. By computing many such simulations, with perturbations at many different depths and locations relative to the wave source, this set of linear equations can be successfully solved numerically for the sensitivity kernels.
Statistical Analysis of Acoustic Wave Power and Flows around Solar Active Regions	Rabello soares, M
M. Cristina Rabello-Soares[1], Richard S. Bogart[2], Philip H. Scherrer[2]
[1]Universidade Federal de Minas Gerais, [2]Stanford University
We analyze the effect of a sunspot in its quiet surroundings applying a helioseismic technique on almost three years of Helioseismic and Magnetic Imager (HMI) observations obtained during solar cycle 24 to further study the sunspot structure below the solar surface. The attenuation of acoustic waves with frequencies lower than 4.2 mHz depends more strongly on the wave direction at a distance of 6°–7° from the sunspot center. The amplification of higher frequency waves is highest 6° away from the active region and is largely independent of the wave’s direction. We observe a mean clockwise flow around active regions, the angular speed of which decreases exponentially with distance and has a coefficient close to ‑0.7 degree‑1. The observed horizontal flow in the direction of the nearby active region agrees with a large-scale circulation around the sunspot in the shape of cylindrical shell. The center of the shell seems to be centered around 7° from the sunspot center, where we observe an inflow close to the surface down to ∼2 Mm, followed by an outflow at deeper layers until at least 7 Mm.
Near-Surface Flow Anomalies in Solar Cycle 24 As Determined By Ring-Diagram Analysis	Baldner, C
Charles Baldner [1], Sarbani Basu [2], Richard Bogart [1], Rachel Howe [3]
[1] Stanford University, [2] Yale University, [3] University of Birmingham
Small variations relative to long term mean flows in the near-surface layers of the Sun can be detected and characterized using local helioseismology. Some of these anomalies appear to be related to the progression of the solar cycle, others have significantly shorter timescales. In this work we exploit eight years of high resolution data from the Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) spacecraft covering the majority of solar cycle 24. We employ ring diagram analysis to measure flow anomalies throughout the shallowest 20Mm of the solar convection zone. We explore, in particular, the asymmetry in flows between the northern and southern hemispheres to search for signs of the onset of the solar cycle 25 torsional oscillation. We also further study persistent high latitude flow anomalies that have been previously detected.
A fragile detection of solar g-modes	Schunker, H
Hannah Schunker[1], Jesper Schou[1], Patrick Gaulme[1], Laurent Gizon [1,2]
[1] Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen [2] Georg-August-Universität Göttingen, Institut für Astrophysik, Friedrich-Hund-Platz 1, 37077 Göttingen
The most recent claimed detection of g-mode oscillations in the Sun using SOHO-GOLF observations has regenerated the field of helioseismology to probe the core of the Sun. I will show that the most recent claimed detection of g-modes is fragile, and highlight the parameters in the analysis method that are the most important for the detection. Moreover, I will show that the g-mode detection is extremely sensitive to the start time of the GOLF time series.

Session 4 - Data-driven modeling of solar atmosphere and solar explosive events

Conveners: Meng Jin (LMSAL), Véronique Delouille (ROB)

Soft X-ray (0.1 – 2.5 nm) Spectral Emission Lines Associated with AR 12713 Observed with Rocket EVE/SAM Instrument on June 18, 2018	Didkovsky, L
Leonid Didkovsky[1], Tom Woods[2], Phil Chamberlin[2], Andrew Jones[2]
[1]University of Southern California, Space Sciences Center (USA), [2]University of Colorado in Boulder, Laboratory for Atmospheric and Space Physics (USA)
Some observations of soft X-ray emission spectral lines associated with AR 12713 are reported in a wavelength range of about 0.1 to 2.5 nm. The spectra were received from a modified EVE/SAM instrument during sounding rocket flight (NASA 36.336 US) launched on June 18, 2018 from the White Sands Missile Range, NM. The modification of the SAM instrument consisted in assembling on it a diffraction transmission grating, which creates a number of spectra from a bright solar disk object like an AR. Such spectra with a good spatial resolution (AR only) and sufficient spectral resolution may help us to model solar reference spectra for more accurate calculations of absolute solar irradiance in soft X-ray.
Observations and Modeling of a High-Latitude, Extended Filament Channel Eruption	Lynch, B
B. J. Lynch[1], E. Palmerio[2], M. D. Kazachenko[1,3], J. Pomoell[2], E. K. J. Kilpua[2]
[1] Space Science Laboratory, Univ. of California-Berkeley, Berkeley, CA, USA, [2] Department of Physics, Univ. of Helsinki, Helsinki, Finland, [3] Laboratory Atmospheric Space Physics, Univ. of Colorado, Boulder, CO, USA
We present observations and modeling of the magnetic field configuration, morphology, and dynamics of a high-latitude, extended filament channel eruption observed by SDO. We analyze the 2015 July 10 filament eruption by quantifying a number of physical properties of the CME source region and the CME's evolution through the corona. The resulting slow streamer blowout CME gives rise to the formation of an extended post-eruption arcade above the polarity inversion line that is only poorly visible in disk observations and does not resemble the typical bright post-eruption loop systems. We estimate the reconnection flux from this "stealthy" flare arcade growth and examine the magnetic field orientation and evolution of the erupting prominence. We present preliminary results from our data-inspired numerical MHD modeling of this event and their comparison to the SDO/AIA observations, focusing on the transition from an erupting sheared-arcade prominence to a slow streamer blowout flux rope CME. The ambiguous on-disk signatures in certain wavelengths suggest that the "stealth CME" phenomenon (and classification) may be more of a continuum of observable or non-observable signatures rather than a distinct type of eruption. As such, these CME events may also be problematic for space weather forecasting.
Global Magnetohydrodynamics Simulation of EUV Waves and Shocks from the X8.2 Eruptive Flare on 2017 September 10	Jin, M
Meng Jin[1,2], Wei Liu[1], Mark Cheung[1], Nariaki Nitta[1], Ward Manchester[3], Leon Ofman[4], Cooper Downs[5], Vahe Petrosian[6], Nicola Omodei[6]
[1]LMSAL, [2]SETI Institute, [3]University of Michigan, [4]NASA Goddard Space Flight Center, [5]Predictive Science Inc., [6]Stanford University
As one of the largest flare-CME eruptions during solar cycle 24, the 2017 September 10 X8.2 flare event is associated with spectacular global EUV waves that transverse almost the entire visible solar disk, a CME with speed > 3000 km/s, which is one of the fastest CMEs ever recorded, and >100 MeV Gamma-ray emission lasting for more than 12 hours. All these unique observational features pose new challenge on current numerical models to reproduce the multi-wavelength observations. To take this challenge, we simulate the September 10 event using a global MHD model (AWSoM: Alfven Wave Solar Model) within the Space Weather Modeling Framework and initiate CMEs by Gibson-Low flux rope. We conduct detailed comparisons of the synthesized EUV images with SDO/AIA observations of global EUV waves. We find that the simulated EUV wave morphology and kinematics are sensitive to the orientation of the initial flux rope introduced to the source active region. An orientation with the flux-rope axis in the north-south direction produces the best match to the observations, which suggests that EUV waves may potentially be used to constrain the flux-rope geometry for such limb or behind-the-limb eruptions that lack good magnetic field observations. We also compare observed and simulated EUV intensities in multiple AIA channels to perform thermal seismology of the global corona. Furthermore, we track the 3D CME-driven shock surface in the simulation and derive the time-varying shock parameters together with the dynamic magnetic connectivity between the shock and the surface of the Sun, with which we discuss the role of CME-driven shocks in the long-duration Gamma-ray events.
Fast velocities of flare ribbon kernels and ribbon elongation in a quiescent filament eruption of 2012 August 31 observed by SDO/AIA	Lorincik, J
Juraj Lörinčík[1][2], Jaroslav Dudík[1], Jana Kašparová[1], Guillaume Aulanier[3], Alena Zemanová[1], Elena Dzifčáková[1]
[1]Astronomical Institute, CAS, Ondřejov, Czech Republic; [2]Institute of Astronomy, Charles University, Prague, Czech Republic; [3]LESIA, Observatoire de Paris, Meudon, France
We report on SDO observations of an eruption of a quiescent filament from 2012 August 31. In the 1600 \AA{} filter channel of AIA, flare ribbons were observed to elongate at velocities up to 480 km s^{-1} and flare kernels move along a ribbon at velocity of $\approx$ 260 km s^{-1}. In order to investigate the emission observed in the 1600 \AA{} channel, we used synthetic spectra modeled using CHIANTI and RADYN models of flare atmospheres with beam parameters constrained using fits of \textit{RHESSI} spectra. We found out that depending on parameters of heating of a flare model, thickness of a region where the emission of the 1600 \AA{} filter channel originates ranges between 10^{-2} and 10^{2} km. Information on dimensions of the formation region were then utilized to estimate densities in flare ribbons using inversions of the emission measure. These were found to range between 10^{10} – 4.10^{12} cm^{-3} for flare atmospheres heated by beams of different parameters. Together with B_{LOS} data from \textit{SDO}/HMI, diagnosed densities were used to calculate Alfvén velocities in observed ribbons. These can be as small as 17 km s^{-1} for flare ribbons observed in region of weak magnetic field at latter stages of heating. This finding suggests that elongation of ribbons and motion of kernels might not be related to waves. Motions along the PIL are well-described in the 3D model of solar eruptions of Aulanier et al. 2013 (A&A, 543, 110). However, EUV observations of flare loops revealed that velocity of their apparent slipping motion is much lower than velocity of elongation of a ribbon, which is observed in a close vicinity. Therefore, observed phenomena can not be directly related to super-Alvénic regime of magnetic slipping reconnection introduced in the 3D model.
Eruptions from quiet Sun coronal bright points: Observations & Modeling	Madjarska-theissen, M
Maria S. Madjarska[1], Klaus Galsgaard[2], Chauzhou Mou[3]
[1]Max Planck Institute for Solar System Research, Goettingen, Germany, [2] Niels Bohr Institute, Copenhagen, Denmark, [3]Institute of Space Sciences, Shandong University, Weihai, China
We present a two part study that aims first to observationally explore in full detail the morphological and dynamical evolution of eruptions from coronal bright points (CBPs) in the context of the full lifetime evolution of 11 CBPs. Next, we employ data-driven modelling based on a relaxation code to reproduce the time evolution of the magnetic field of these eruptive CBPs, and provide an insight on the possible causes for destabilisation and eruption. Observations of the full lifetime of CBPs in data taken with the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory in four passbands He II 304 Å, Fe IX/X 171 Å, Fe XII 193 Å, and Fe XVIII 94 Å are investigated for the occurrence of plasma ejections, micro-flaring, mini-filament eruptions and mini coronal mass ejections (mini-CMEs). Data from the Helioseismic and Magnetic Imager are analysed to study the longitudinal photospheric magnetic field evolution associated with the CBPs and related eruptions. The magnetic structure of each CBP is then evolved in time using the relaxation approach, based on a time series of HMI magnetograms. This results in a series of Non-Linear Force Free Field Extrapolations (NLFFF). The time series is initiated with a potential field extrapolation based on a HMI magnetogram well before the eruptions, and evolved in time as a response to the changes in the magnetic field distribution in the photosphere. This time series of NLFFF field solutions is analysed for the local and global magnetic field structure in the vicinity of the eruption sites.
On the extrapolation of magneto-hydro-static equilibria on the sun: model and tests	Zhu, X
Xiaoshuai Zhu[1], Thomas Wiegelmann[1]
[1] Max Planck Institute for Solar System Research
Modeling the interface region between solar photosphere and corona is challenging, because the relative importance of magnetic and plasma forces change by several orders of magnitude. While the solar corona can be modeled by the force-free assumption, we need to take care about plasma forces (pressure gradient and gravity) in photosphere and chromosphere, here within the magneto-hydro-static (MHS) model. We solve the MHS equations with the help of an optimization principle and use vector magnetogram as boundary condition. Positive pressure and density are ensured by replacing them with two new basic variables. The Lorentz force during optimization is used to update the plasma pressure on the bottom boundary, which makes the new extrapolation works even without pressure measurement on the photosphere. Our code is tested by using a linear MHS model as reference. From the detailed analyses, we find that the newly developed MHS extrapolation not only recovers the plasma distribution at high accuracy. but also gives the better fit magnetic field than the nonlinear force-free extrapolation.
What can we learn from impulsively generated waves observed by SDO/AIA?	Ofman, L
Leon Ofman[1], Wei Liu[2], Tongjiang Wang[3]
[1]NASA Goddard Space Flight Center and CUA, Greenbelt, MD, USA, [2]Lockheed Martin Space and Astrophysics Lab. and Stanford U. and BAERI, Palo Alto, CA, USA
Since the launch of the SDO/AIA instrument in 2010, various types of MHD waves in the solar corona have been observed in unprecedented detail. Notable examples include quasi-periodic fast propagating (QFP) waves in active regions, global EUV waves in the large-scale corona, standing kink and slow magnetosonic waves in coronal loops. The observed waves are generated by impulsive events, such as flares and CMEs, and can range in two orders of magnitude in phase speed from ~100 km/s to >1000 km/s, depending on their types and polarizations. The amplitude of the waves ranges from linear (i.e., with the velocity amplitude being small compared to the phase speed) to nonlinear regimes with shock-like features. The observations of the waves combined with MHD modeling provide a unique means of understanding the propagation/reflection/refraction of the waves and their interactions with coronal structures. We will present recent SDO/AIA observations of impulsively generated coronal waves and related MHD modeling results. We will also present applications of coronal seismology using these waves to determine the magnetic and thermal properties of various coronal structures.
Research on Solar Drivers of Space-weather: Sun-Earth connection of magnetic flux ropes	Vemareddy, P
P. Vemareddy [1], P. Demoulin[2]
[1] Indian Indian Institute of Astrophysics, Bengaluru, India [2] Observatory de Paris, Meudon, LESIA, Paris
I present few representative results of the research on solar drivers of space weather carried out in the past two years. The objectives include how local plasma evolution leads to formation of magnetic flux ropes (MFRs), its eruption and heliospheric evolution. To show this scenario of Sun-earth connection of an MFR, we undertook an eruption event involving clear flux rope signatures on the Sun, and studied its formation, initiation, driving mechanisms. Further, we extended our earlier studies on helicity flux transport in emerging ARs, sun-earth connections of MFR, and sunspot rotation as a driver of major solar eruptions. In an emerging AR, the helicity being pumped by flux emergence and plasma motions revealed that the flux tube is likely having opposite signs of helicity along its length. These results suggest that the ARs with a predominant sign of helicity flux launch CMEs at some point of time, however, the AR with successive injection of opposite helicity exhibits cancellation of coronal helicity leading to field reconfiguration and dissipation of energy heating the corona. The sun-earth connection of a CME is probed by in-situ observations, which delineates the source region magnetic signatures in the magnetic cloud. On the other hand, a rotating sunspot in AR 12158 is proved to have built flux rope like sigmoidal structure by injecting twist, which is apparently co-temporal with the occurrence of two major CMEs.

Session 5 - Frontier: Solar Poles Exploration and new prospects

Conveners: Rebecca Centeno (HAO/NCAR), Barbara Thompson (GSFC)

Exploring The Solar Poles From L1 Perspective	West, M
Matthew West[1]
[1]Royal Observatory of Belgium
Due to the optically thin nature of the EUV solar atmosphere it is possible to recreate images of the solar poles using observations made from the L1 perspective. By combining over half a Carrington rotation worth of EUV observations made with the SWAP (on PROBA2) and AIA (on SDO) EUV imagers with radial and temporal filters, it has been possible to examine structures in the solar polar regions. In this presentation I will show the subtle differences between the structures observed in the different EUV passbands and assess which wavelengths are best for observing the poles, with a perspective for future polar observing missions.
New HMI Data Series: temporally consistent disambiguation for HARP vector magnetic field timeseries data	Barnes, G
Graham Barnes[1], KD Leka[1], Eric Wagner[1]
[1]NWRA
The last step of the HMI pipeline removes the 180 degree ambiguity in the direction of the field transverse to the line of sight, enabling users to download physically meaningful components of the photospheric vector field. However, for the pipeline, each time is treated independently, which can lead to changes in the direction of the transverse field from one time to the next that are unphysical. These changes result in large values of the time derivative of the inferred surface magnetic field vector, and hence spurious changes in quantities such as flows and electric fields computed from it. NWRA has developed an enhanced version of the disambiguation code that includes a temporal consistency term. We compare the results of the new method to the results of the pipeline code and demonstrate the improvement in temporal stability. A new data product with the time-series disambiguation is being made available to the community through the JSOC for selected HARPS. This material is based upon work supported by NASA under award Nos. 80NSSC18K0055 and 80NSSC18K0180.
NuSTAR’s observations of tiny flares and big eruptions	Hannah, I
Iain Hannah[1], Brian Grefenstette[2], Lindsey Glesener[3], Sam Krucker[4,5], David Smith[6], Hugh Hudson[1,4], Stephen White[7], Matej Kuhar[5]
[1]Glasgow, [2]Caltech, [3]Minnesota, [4]Berkeley, [5]FHNW, [6]Santa Cruz, [7]AFRL
NuSTAR is an astrophysics X-ray telescope, with direct imaging spectroscopy providing a unique sensitivity for observing the Sun above 2.5keV. Targeting the faintest X-ray emission from the solar atmosphere allows the study of the smallest flares, and their contribution to heating the corona. However, it can also be used to observe weak high-coronal sources that are associated with the energy release in large, but occulted, eruptions. NuSTAR has observed the Sun over a dozen times since Sep 2014, through to our latest observations in 2018: see http://ianan.github.io/nsovr/ for a quicklook overview of NuSTAR’s solar observations. We will present some of the latest solar observations with NuSTAR and compare them to the emission seen at lower energy wavelengths, particularly in EUV with SDO/AIA and also the derived Fe18 emission.
The butterfly diagram and tilt angles obtained from the Horrebow sunspot observations	Valliappan, S
Senthamizh Pavai Valliappan [1], Rainer Arlt [1], Christoffer Karoff [2,3], Carsten Sønderskov Jørgensen [3]
[1] Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany, [2] Department of Geoscience, Aarhus University, Høegh-Guldbergs Gade 2, 8000, Aarhus C, Denmark, [3] Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000, Aarhus C, Denmark
The solar dynamo is not fully periodic (and monotonous) as the solar cycles exhibit mild to extreme variability in their characteristics. The study of properties of sunspots over centuries may enable deeper understanding of the solar dynamo and to predict the next solar cycles. The scattered records of sunspot observations, since the invention of the telescope, are not completely inspected yet. The discovery and analysis of many old records of sunspot observations are currently ongoing and they reveal interesting properties of solar cycles. We are currently analyzing the record of sunspot observations by Christian Horrebow from the Copenhagen observatory during 1761 – 1777. The sunspot record by Horrebow has already been analyzed by Thiele (1859), Wolf (1873), and Hoyt & Schatten (1995), but they only studied the sunspot numbers. However, the sunspot record also contains the positions of sunspots, even though not the area measurements, which we are analyzing now. The positions of sunspots are very important parameters in constraining the solar dynamo, in particular the tilt angles of sunspot groups can be calculated if the individual sunspot positions are available. The tilt angles of sunspot groups are also an important parameter in the flux transport dynamo model, in which it determines the evolution of the polar field which in turn determines the properties of next solar cycle. In Horrebow’s sunspot record, the positions of sunspots are given in tables containing the horizontal position readings in units of sidereal time, corresponding to the passage to the solar disk, and the vertical position readings in screw turns of the instrument used. The butterfly diagram is constructed with the obtained positional readings of sunspots for the solar cycles 1 (maximum), 2, and 3 (beginning). We group the sunspots into groups and then calculate the tilt angles of sunspot groups. The sunspot positions and tilt angles for cycles 1 – 3 are also available independently from the sunspot drawings of Staudacher, which are comparatively not very precise and lack orientation but cover a longer period than Horrebow’s. The properties of solar cycles from two independent records are compared and the reliability of Staudacher’s drawings is determined.
The Role of the Solar Soft X-ray Irradiance on Thermospheric Chemistry and Structure	Samaddar, S
Srimoyee Samaddar[1], Karthik Venkataramani[2], Scott Bailey[3]
[1]Virginia Polytechnic Institute and State University, [2]Virginia Polytechnic Institute and State University, [3]Virginia Polytechnic Institute and State University
The solar soft x-ray irradiance deposits energy into the lower thermosphere, thus playing a significant role in the photochemistry and E-region ionosphere. Since the irradiance varies strongly with solar activity, it is imperative to incorporate this variability in models predicting the earth’s thermosphere. In this talk, we use the recently developed ACE1D model to explore the role of solar soft x-rays on temperature, chemistry, and the overall structure of the thermosphere. The ACE1D model produces a global average thermosphere by self- consistently solving the one-dimensional continuity equations to obtain the ions and neutral densities and the energy equations to obtain the ions, neutral and electron temperatures. A combination of solar and magnetospheric fluxes and joule heating is used as energy inputs to the model. We show that solar soft X-rays are the dominant driver of globally averaged nitric oxide densities. We further find that the soft x-rays have a very large impact on temperature throughout the thermosphere, even though their energy is deposited low in the thermosphere. We show that this is due to the heat exchange from non-thermal electrons which plays a significant part in energy dynamics of the thermosphere.
New and Improved Mode Fitting Results	Korzennik, S
Sylvain G. Korzennik
Harvard-Smithsonian Center for Astrophysics
I present the most recent improvements to my mode fitting procedures, and how they affect inferred properties of the Sun. The fitting has now been extended to $\ell=0$ modes, and in the process to more $\ell=1$ modes. Close scrutiny of these low degree modes revealed the need to change the scaling of the error bars on the derived multiplet quantities. I fitted a test data set using different leakage matrices, including one set computed to fit very long time series and therefore uses for $B_o$ the value of $5.0593^o$ (or $\sqrt{|Bo^2|}$). I show how that leakage matrix is different from the one computed in the past for very long time series ($B_o=0$) and its impact on the fitted parameters.
Variation in Sun's Seismic Radius and its implication on the TSI variability	Tripathy, S
Kiran Jain, Sushanta Tripathy, Frank Hill
National Solar Observatory, Boulder, Co 80303 USA
Space-borne instruments on-board SoHO and SDO have been collecting uninterrupted helioseismic data since 1996 and are providing a unique opportunity to study changes occurring below the surface over two solar cycles, 23 and 24. Here we study the variation in solar seismic radius with the changing level of the surface magnetic activity. The seismic radius is calculated from the fundamental modes of solar oscillations utilizing the observations from SoHO/MDI and SDO/HMI. Our study suggests that the sub-surface layers shrinks with increasing magnetic activity. We interpret these changes in seismic radius to be caused by the variation of sound speed, temperature or the changes in the super-adiabatic superficial layers. Our estimated maximum change in seismic radius during a solar cycle is about 5 kilometers, and is consistent in both solar cycles 23 and 24. We also explore the relationship between seismic solar radius and the total solar irradiance (TSI) and find that the radius variation plays a secondary role in TSI variability. We further observe that the solar irradiance increases with decreasing seismic radius, however the anti-correlation between them is moderately weak.

Session 6 - Magnetic structure of the corona and its transition to the heliosphere

Conveners: David Berghmans (ROB), Marc DeRosa (LMSAL)

Exceptional Extended Field of View Observations by SWAP on 1 and 3 April 2017	O'hara, J
Jennifer O'Hara[1], Marilena Mierla[1,2], Elena Podladchikova[1], Elke D'Huys[1], Matthew J West[1]
[1]Solar–Terrestrial Center of Excellence – SIDC, Royal Observatory of Belgium, Brussels, Belgium, [2]Institute of Geodynamics of the Romanian Academy, Bucharest, Romania
On the 1st and 3rd April 2017 two large solar eruptions, which were associated with an M4.4 and M5.8 class flare, respectively, were observed on the solar western limb with the PROBA2/SWAP telescope. The large field of view of SWAP combined with the exceptional circumstances of the satellite being off-pointed in a favorable position to view the events, provide us with the rare opportunity to study these eruptions up to approximately 2 solar radii, where space-based coronagraph observations begin. SWAP observations reveal off-limb erupting features as well as on disk EUV waves initiated by these eruptions. Using this unique set of observations, the evolution of these two events is tracked and the propagating speeds of both the eruptions and the on-disk EUV waves are calculated.
Solar Coronal Jets Extending beyond the AIA Field of View Observed during the 2017 August 21	Hanaoka, Y
Y. Hanaoka[1,2], R. Hasuo[1,2], T. Hirose[2], A. C. Ikeda[2], T. Ishibashi[2], N. Manago[2], Y. Masuda[2], S. Morita[2,3], J. Nakazawa[2], O. Ohgoe[1,2], Y. Sakai[2,4], K. Sasaki[2], K. Takahashi[3], and T. Toi[2]
[1]National Astronomical Observatory of Japan, [2]Solar Eclipse Digital Imaging and Processing Network, [3]NPO Kwasan Astro Network, [4]Chiba Prefectural Tsurumaisakuragaoka High School
We observed six polar coronal jets extending beyond 2 Rsun during the solar eclipse on 2017 August 21 in white-light images. All of them were found in polar plumes as narrow structures above EUV jets observed in the low corona observed with the AIA of the SDO. The EUV observation shows much more jets, but the jets whose brightnesses are comparable to ordinary soft X-ray jets and that occurred in the polar regions near the eclipse period were observed as eclipse jets without exception. These results mean that the ordinary polar jets actually extend beyond the field-of-view of the AIA and probably escape from the Sun as part of the solar wind. Solar eclipse observations enable us to observe the corona between about 1.2-2.0 Rsun, which is difficult to observe with the current spaceborne instruments. Observing beyond the AIA field-of-view is promising to know the larger scale aspects of the coronal dynamic phenomena seen in the low height.
Long-term evolution of the solar corona using SWAP data	Mierla, M
Marilena Mierla[1,2], Elke D’Huys[1], Daniel B. Seaton[3], David Berghmans[1], Matt West[1], Elena Podladchikova[1], Laurence Wauters[1], Jan Janssens[1]
[1] Royal Observatory of Belgium, Brussels, Belgium, [2] Institute of Geodynamics of the Romanian Academy, Bucharest, Romanian, [3] NOAA, Boulder, USA
In this work, we use the PROBA2/SWAP images to study the evolution of the large-scale structures of the solar corona observed in the EUV during the solar cycle 24 (from 2010 to 2018). We will discuss the evolution of the corona at different heights above the solar surface and the evolution of the corona over the poles. We compare it with the sunspot number evolution.
Reflection of Acoustic Modes on Sunspots	Waidele, M
Matthias Waidele, Kolja Glogowski, Markus Roth
Kiepenheuer-Institut für Sonnenphysik
Sunspots are known to strongly influence solar acoustic modes. There is a variety of possible interactions of the magnetic field and the waves, one of them being reflection. Assuming that part of a wave got reflected at the subsurface magnetic fluxtube it should be detectable at the surface again. In our studies we use the helioseismic Fourier-Hankel analysis method to decompose sunspot data of 6 days recorded by SDO/HMI into in and outgoing waves. The power spectrum of outgoing waves shows a signal that could theoretically be contributed to wave reflection at the sunspot.
Power spectrum power-law indices as a diagnostic of coronal heating	Ireland, J
Jack Ireland[1], Nicholeen Viall[2], Stephen Bradshaw[3], Michael Kirk[4]
[1] ADNET Systems, Inc., MD, USA / NASA GSFC, MD, USA, [2] NASA GSFC, [3] Rice University, TX, USA, [4] Catholic University, DC, USA.
We investigate the coronal heating of active regions by bringing together novel data analysis techniques with hydrodynamic modeling in a new and unique way. Viall & Klimchuk 2011, 2012, 2014, 2017 have shown that the timing of active region coronal emission brightenings in multiple channels of Solar Dynamics Observatory Atmospheric Imaging Assembly (SDO/AIA) follows that expected from simulations of a nanoflare-heated corona. Using Numerical HYDrodynamic RADiative Emission Model for the Solar Atmosphere (HYDRAD)-based simulations of AIA emission for an AR, Bradshaw & Viall 2016 have shown that the timing of coronal emission brightenings is dependent on the properties of the nanoflare energy distribution and occurrence rate. Relatedly, Ireland et al. 2015 show that average power spectra $P(f)$ (where $f$ is frequency) of time series of AIA 171Å and 193Å AR images are dominated by power laws, $P(f)~f^{-z}, z>0$. Ireland et al. 2015 show that a distribution of exponentially decaying events of emission $E$ along the line-of-sight, where $N(E)~E^{-m}$ and the size of the emission depends on its duration $T$ such that $E~T^{k}$ creates a power law power spectrum $P(f)~f^{-k(2-m)}$. We present analyses that test the hypothesis that a distribution of nanoflare events causes both the emission power-law power spectrum in AIA time-series as well as the observed brightening time-lags. Firstly, we show that the power-law indices of Fourier power spectra of the same simulated data described in Bradshaw & Viall 2016 depends on the frequency of nanoflares used. Secondly, using the same observational AIA time-series data analyzed by Viall & Klimchuk (2012), we obtain correlations of the cross-channel time-lags with the power-law indices of Fourier power spectra in each AIA channel. Finally, the ability of power-law indices and time-lags together to constrain the underlying nanoflare frequency distribution is discussed.
On the Vertical Magnetic Field at the Umbral Boundary of a long-lived Sunspot	Schmassmann, M
Markus Schmassmann, Rolf Schlichenmaier, Nazaret Bello {Gonz\'alez}
Kiepenheuer-Institut fuer Sonnenphysik (KIS), Freiburg i.Br., Germany
In a statistical study of sunspots in 79 active regions observed with SP/Hinode, {Jur{\v c}{\'a}k}~et~al.\ (2018) found no dependence on sunspot size of the vertical magnetic field component $B_\text{ver}$ averaged along the umbral boundary. They concluded that the absolute value of $B_\text{ver}$ at the umbral boundary is the same for all spots. We present here our investigation of the temporal evolution of $B_\text{ver}$ averaged along the umbral boundary of one long-lived sunspot during its stable phase. We use HMI/SDO data of the full disc passage of NOAA AR 11591. Contours of continuum intensity at $I_\text{c}=0.5I_\text{qs}$, whereby $I_\text{qs}$ refers to the average over the quiet sun areas, are used to extract the magnetic field along the umbral boundary. Projection effects due to different formation heights of the Fe\,\textsc{i}~617.3\,nm line and continuum are taken into account. We find that during the first disc passage, $B_\text{ver}$ remains constant at 1693\,G with a root-mean-square deviation of 15\,G, whereas the magnetic field strength varies substantially (mean 2171\,G, rms of 48\,G) and shows a long term variation. Compensating for formation height has little influence on the mean value along each contour, but reduces the variations along the contour when away from disc centre, yielding a better match between the contours of $B_\text{ver}=1693\,$G and $I_\text{c}=0.5I_\text{qs}$. We will show that during the disc passage of a stable sunspot, its umbral boundary can equivalently be defined by using the continuum intensity $I_\text{c}$ or the vertical magnetic field component $B_\text{ver}$, while contours of fixed magnetic field strength fail to outline the umbral boundary.
Multi-wavelength Observations of Flare-Induced Acoustic Waves Around Active Regions with SDO AIA	Pesnell, D
Teresa Monsue[1], W. Dean Pesnell[2], Frank Hil[3]l, Michael Kirk[2]
[1] Vanderbilt University, Nashville, Tennessee, USA [2] NASA GSFC, Greenbelt, Maryland, USA [3] NSO, Boulder, Colorado, USA
Active regions on the Sun are abundant with a variety of waves that are both acoustically helioseismic and magnetohydrodynamic in nature. The occurrence of a solar flare can disrupt these waves, through MHD mode-mixing or scattering by the excitation of these waves. We take a multi-wavelength observational approach to understand the source of these waves by studying active regions where flaring activity occurs. Utilizing a Fast Fourier Transform (FFT) algorithm, our approach is to search for signals within a time series of images by producing multi-frequency power map movies and spatially sampling the time series by radial sectors with constant area that minimizes the spatial variation of the acoustic power. With this application we are able to study the active region both spatially and temporally and correlate data over multiple wavelengths, allowing us to observe the behavior of the waves at different heights within the Solar atmosphere. We apply multi-wavelength measurements utilizing NASA’s SDO AIA 1700 (lower photosphere), 1600 (upper photosphere) and 304 (chromosphere) passbands. When we run power map movies of the chromosphere we are able to see a subtle propagating feature moving outward from the center of the flare; this could be an MHD-wave propagating outward by the flaring event. With our sector sampling method we observe power variation around the flaring active region. This power variation corresponds to the flare induced enhancement of the oscillations around the active region. Furthermore, there seems to be absorptive properties observed within the chromospheric line of the AIA 304 \AA\ passband.
The spectral content of SDO/AIA 1600 and 1700 A filters from flare and plage observations	Milligan, R
Paulo Simoes[1,2], Hamish Reid[1], Ryan Milligan[1,3,4], Lyndsay Fletcher[1]
[1]University of Glasgow, [2]Centro de Radio Astronomia e Astrofisica Mackenzie, [3]NASA Goddard Space Flight Center, [4]Department of Physics Catholic University of America
The strong enhancement of the ultraviolet emission during solar flares is usually taken as an indication of plasma heating in the low solar atmosphere caused by the deposition of the energy released during these events. Images taken with broadband ultraviolet filters by the Transition Region and Coronal Explorer (TRACE) and Atmospheric Imaging Assembly (AIA 1600 and 1700 \AA) have revealed the morphology and evolution of flare ribbons in great detail. However, the spectral content of these images is still largely unknown. Without the knowledge of the spectral contribution to these UV filters, the use of these rich imaging datasets is severely limited. Aiming to solve this issue, we estimate the spectral contributions of the AIA UV flare and plage images using high-resolution spectra in the range 1300 to 1900 \AA\ from the Skylab NRL SO82B spectrograph. We find that the flare excess emission in AIA 1600 \AA\ is composed of the C IV 1550 \AA\ doublet (26\%), Si I continua (20\%), with smaller contributions from many other chromospheric lines such as C I 1561 and 1656 \AA\ multiplets, He II 1640 \AA, Si ii 1526 and 1533 \AA. For the AIA 1700 \AA\ band, C I 1656 \AA\ multiplet is the main contributor (38\%), followed by He II 1640 (17\%), and accompanied by a multitude of other chromospheric lines, with minimal contribution from the continuum. Our results can be generalized to state that the AIA UV flare excess emission is of chromospheric origin, while plage emission is dominated by photospheric continuum emission in both channels.

Session 7 - Machine Learning and Forecasting

Conveners: Véronique Delouille (ROB), Meng Jin (LMSAL)

Supervised Neural Networks for Helioseismic Ring-diagram Inversions	Hanson, C
Rasha Alshehhi[1], Chris S. Hanson[2], Laurent Gizon[2,3,1]
[1]Center for Space Science NYUAD Institute New York University Abu Dhabi UAE, [2]Max Planck Institute for Solar system research, G{\"o}ttingen, Germany, [3] Institut f{\"u}r Astrophysik, Georg-August-Universit{\"a}T G{\"o}ttingen, Germany
The inversion of ring fit parameters to obtain subsurface flow maps in ring-diagram analysis for SDO observations is computationally expensive. We apply machine learning techniques to the inversion step of the pipeline, to replace future inversion requirements. We utilize Artificial Neural Networks as a supervised learning method for predicting the flows in $15^\circ$ ring tiles. To demonstrate that the machine learning results still contain the subtle signatures key to local helioseismic studies, we use the machine learning results to re-detect equatorial Rossby waves. We find the Artificial Neural Network is computationally efficient, can achieve a root mean-square error of half that reported for the observations, and reduce computational burden by two orders of magnitude. We find that the signatures of the Rossby waves are still in the machine learning results, showing that important helioseismic signatures are maintained.
Extracting Solar Physics from 151 Million EUV Images	Kirk, M
Michael S. Kirk[1], Barbara Thompson[2], Raphael Attie[3], Nicki Viall-Kepko[2], Peter Young[4]
[1]NASA GSFC / Catholic University of America, [2]NASA GSFC, [3]NASA GSFC / NPP, [4]NASA GSFC / GMU
Beginning in 2010, the Solar Dynamics Observatory's Atmospheric Imaging Assembly (SDO AIA) revolutionized solar imaging with its high temporal and spatial resolution and coverage. The archive of extreme ultraviolet (EUV) images is now over 150 million and continues to grow. Automated algorithms consistently clean these images to remove magnetospheric particle impacts on the CCD cameras, but it has been found that compact, intense solar brightenings are often removed as well. There are now over 3 trillion "spiked pixels" that have been removed from EUV images. We estimate that 0.001% of those are of solar origin and removed by mistake – an unexplored dataset of about 30 million events. We take a novel approach and survey the entire set of AIA "spike" data to identify and group compact brightenings across the entire SDO mission. We then use the spike database to form statistics on compact solar brightenings without having to process large volumes of full-disk AIA data. The qualities of the “spikes” with a solar origin represent the most complete archive of compact EUV bright points ever assembled.
Irradiance Coronal Dimming and its Connection to CME Kinetics	Mason, J
James Paul Mason[1], Nick Arge[1], Larisza Krista[2], Alysha Reinard[3], Barbara J. Thompson[1], David F. Webb[4], Jake Wilson[5], Thomas N. Woods[6]
[1]NASA Goddard Space Flight Center, [2]University of Colorado / CIRES, Boulder, CO, USA, [3]NOAA/ SWPC, Boulder, CO, USA, [4]Boston College Institute for Scientific Research 5University of Maryland, College Park, USA, [6]University of Colorado at Boulder Laboratory for Atmospheric and Space Research
When coronal mass ejections (CMEs) depart the corona, they leave behind a transient void. Such a region evacuated of plasma is known as a coronal dimming and it contains information about the kinetics of the CME that produced it. The dimming can be so great in the extreme ultraviolet (EUV) that it reduces the overall energy output of the sun in particular emission lines, i.e., dimming is observable in spectral irradiance. We use the Solar Dynamics Observatory (SDO) EUV Variability Experiment (EVE) data to search for and parameterize dimming. We focus our search on the 39 extracted emission lines data product. We are searching these light curves for dimming around all of the >8,500 ≥C1 solar flares in the SDO era. Our method of combining these 39 light curves to remove the flare peak results in 1,521 light curves for every solar flare. Thus, we come to a total of ~13 million light curves in which to search for dimming. The question is: which ones are sensitive to CME-induced dimming? To answer this and related questions, I’m using machine learning techniques built into python’s scikit-learn library. I will describe the results of applying these techniques to the EVE data to produce the catalog, to the catalog itself, and to comparisons with other related catalogs. All of the code is open source python available on GitHub (https://github.com/jmason86/James-s-EVE-Dimming-Index-JEDI).
Coronal holes detection using supervised classification	Delouille, V
Veronique Delouille (STCE/Royal Observatory of Belgium) Veronique Delouille[1], Stefan Hofmeister[2], Martin Reiss[3], Benjamin Mampaey[1], Manuela Temmer[2], Astrid Veronig [2]]
[1]Royal Observatory of Belgium, Belgium, [2]University of Graz, Austria, [3]Space Research Institute, Graz, Austria
We demonstrate the use of machine learning algorithms in combination with segmentation techniques in order to distinguish coronal holes and filaments in solar EUV images. We used the Spatial Possibilistic Clustering Algorithm (SPoCA) to prepare data sets of manually labeled coronal hole and filament channel regions present on the Sun during the time range 2010-2016. By mapping the extracted regions from EUV observations onto HMI line-of-sight magnetograms we also include their magnetic characteristics. We computed average latitude, area, shape measures from the segmented binary maps as well as first order, and second order texture statistics from the segmented regions in the EUV images and magnetograms. These attributes were used for data mining investigations to identify the most performant rule to differentiate between coronal holes and filament channels, taking into account the imbalance in our dataset which contains one filament channel for 15 coronal holes. We tested classifiers such as Support Vector Machine, Linear Support Vector Machine, Decision Tree, k-Nearest Neighbors, as well as ensemble classifier based on Decision Trees. Best performance in terms of True Skill Statistics are obtained with cost-sensitive learning, Support Vector Machine classifiers, and when HMI attributes are included in the dataset.
Driving Scientific Discovery with Machine Learning and AI at the NASA GSFC Center for HelioAnalytics	Thompson, B
Barbara J. Thompson[1], Michael S. Kirk[1,2], Menelaos Sarantos[1]
[1]NASA Goddard Space Flight Center, USA, [2]Catholic University of America
What is HelioAnalytics? This is a broad term meant to cover all the ways that we harness advanced statistics, informatics and computer science methods to achieve our science. Our focus is on problems that we can attack with modern methods that we cannot attack otherwise. A keener understanding of how information is derived from data, and how machine learning can be harnessed to accomplish this, will expand the discovery potential for key heliophysics research topics and missions. We report on a new program to integrate modern information science, statistics, and scientific knowledge to advance the fundamental physics of connected sun-heliosphere-geospace system. The Center for HelioAnalytics is an “expert group” at NASA GSFC focusing on topics such as machine learning, neural networks, and data analytics in order to expand the discovery potential for key heliophysics research topics and missions. We define “HelioAnalytics” as a hybrid of Heliophysics + Machine Learning + Statistics + Information Design. Each of these are fields that are well developed in their own right; HelioAnalytics is the cross-disciplinary convergence of communities of physicists, statisticians, and computer scientists. HelioAnalytics is intended to foster research into advanced methodologies for heliophysical research, and to promulgate such methods into the broader community.
SHARPs and SMARPs: 22 years of solar active region data	Bobra, M
Monica Bobra
Stanford University
We study 22 years of solar active regions using measurements of the photospheric magnetic field taken by the SoHO/MDI and SDO/HMI instruments. We calculate various properties of these 13548 active regions -- such as size, flux, and topological features -- and determine statistical relationships between these properties and flaring activity. We also analyze 118 active regions from the period between May and October 2010, when both the SoHO/MDI and SDO/HMI instruments took co-temporal measurements of the photospheric magnetic field, to assess if, and how, our calculated properties vary with instrument. Our data series, called Space-weather HMI Active Region Patches, or SHARPs (Bobra et al. 2014), and Space-weather MDI Active Region Patches, or SMARPs (Bobra et al., 2018, in prep), provide seamless coverage of solar active regions spanning two solar cycles from 1996 to the present day.
Estimating solar far-side magnetic flux from STEREO EUV observations by deep learning	Chen, R
Ruizhu Chen[1,2], Junwei Zhao[2]
[1]Physics Department, Stanford University, [2] Hansen Experimental Physics Laboratory, Stanford University
The solar far-side magnetic flux is a crucial observable for space weather forecasting and solar wind modeling. However, such magnetic flux is not directly measured, but can be estimated using the far-side STEREO observations of extreme ultraviolet (EUV) 304 Å flux through the relation between the two quantities established by a machine-learning method. The near-side magnetic flux and EUV 304 Å flux are observed continuously for 8 years by the SDO/HMI and SDO/AIA, respectively, therefore, an image-to-image relation can be built by a deep-learning algorithm using these data. A deep neural network is thus trained using 10,000 calibrated image pairs of the magnetic flux and the EUV flux, sampled from the 8 years of SDO observations. The trained neural network can reproduce the magnetic flux in great details from the EUV flux and with a similarity close to 0.9. We then apply this neural network on the STEREO EUV images, and derive the maps of magnetic flux on the far side.
Photospheric Magnetic Field Properties of Flaring vs. Flare-quiet active regions, V: Results from HMI	Leka, K
KD Leka[1,2], G Barnes [1]
[1] NorthWest Research Associates, [2] Nagoya University / Institute for Space-Earth Environmental Research
What constitutes the difference between those solar active regions that produce energetic events and those that do not? The answer no doubt lies in the state and ongoing evolution of the magnetic field. Extending this series of studies of the photospheric magnetic field as related to flare imminency, we consider daily evaluations of almost all HMI Active Region Patches (HARPS), including temporal evolution. Using the NWRA Classification Infrastructure based on NonParametric Discriminant Analysis, we evaluate not only the static characterization of the photospheric field (extending well beyond the SHARP parameters) but include coronal topology and time-series considerations, as well. Additionally, we extend the analysis beyond "global" parametrizations to describe sub-area sites which may play roles in coronal energization and event triggering. We report here on those parametrizations which best distinguish imminent flaring from imminent quiet sunspot groups.
A deep learning approach to forecast tomorrow's solar wind parameters.	Shneider, C
Carl Shneider[1], Mandar Chandorkar[1], Monica Bobra[2], Enrico Camporeale[1]
[1] Centrum Wiskunde & Informatica, [2] Stanford University
Deep learning has proven extremely successful both in classification and regression problems, especially when it is trained on very large datasets. In the Space Weather context, despite the unarguably large amount of data at our disposal, it remains an open question whether historical datasets contain enough information to build a predictive deep learning system. In this work, we use multi-wavelength solar images from both SDO (Solar Dynamics Observatory) and SOHO (Solar and Heliospheric Observatory) as inputs to a convolutional neural network, to predict solar wind parameters observed at L1, 24 hours ahead.
AI-generated EUV images from SDO/HMI magnetograms by deep learning	Park, E
Eunsu Park[1], Yong-Jae Moon[1], Harim Lee[1]
[1]School of Space Research, Kyung Hee University
In astronomy and geophysics, multi-wavelength observations become very popular. Recently, several deep learning methods for image-to-image translations have been suggested and are successful for different types of transformation such as labels to street scene, black and white images to color ones, aerial to map, day to night, and sketch images to pictures. In this study, we apply an image-to-image translation model, based on conditional Generative Adversarial Networks (cGANs), to construct solar EUV images using solar magnetograms. For this, we train the model using pairs of SDO/AIA EUV image and their corresponding SDO/HMI line-of-sight magnetogram for all AIA wavelengths from 2011 to 2017 except September and October. We test the model by comparing pairs of actual SDO/AIA EUV images and corresponding AI-generated ones in September and October. We find that both real and AI-generated images are quite consistent with each other in that it is difficult for one to distinguish solar EUV images from AI-generated ones. Especially, 193 and 211 data sets have the best average correlation values (0.91) between actual EUV images and AI-generated ones for test data sets, being consistent with the idea that the origin of coronal heating is magnetic field. Using this model, we have a plan to construct solar EUV images with Kitt peak magnetograms since 1974. This methodology can be applicable to many scientific fields that use several different filter images.
Combining sparsity DEM inversions with event tracking for AIA data	Bethge, C
Christian Bethge[1], Amy Winebarger[2], Sanjiv Tiwari[3,4]
[1]Universities Space Research Association, Huntsville, AL, [2]NASA Marshall Space Flight Center, Huntsville, AL, [3]Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, CA, [4]Bay Area Environmental Research Institute, NASA Research Park, Moffett Field, CA
We apply a modified event tracking code (ASGARD - \emph{Automated Selection and Grouping of events in AIA Regional Data}) to the results from sparsity DEM inversions (Cheung et al, 2015) using AIA EUV data. Outputs are grouped regions (x/y/t) in multiple defined temperature bins that can then be correlated in space and time to track the thermal evolution of coronal structures. We show examples and an overview of the methodology.

Session 8 - Solar/stellar magnetic activity and its influence on planetary bodies

Conveners: James Mason (GSFC), Marc DeRosa (LMSAL)

Latitudinal variability of Total electron content over low, mid and high latitudes during solar maximum and its comparison with IRI-2012 and IRI-2016 model	Atulkar, R
Roshni Atulkar[1],P.K. Purohit[2]
National Institute of Technical Teachers' Training and Research, Bhopal, 462002,MP, India.[1],National Institute of Technical Teachers' Training and Research, Bhopal, 462002,MP, India.[2]
Total electron content (TEC) is a key of ionospheric parameters which is defined as the total number of electrons present within a cross-section 1 m2 along the integrated path from the satellite to the receiver. TEC describes the major impact of the ionosphere on the propagation of radio waves which is crucial for terrestrial and Earth space communication including Global Positioning System (GPS). For this analysis we used dual frequency GPS observations at low, mid and high latitude stations IISC, Bangalore, India (13.02_N, 77.57_E), GUAO, Urumqi, China (43.82_N, 87.60_E) and NYAL, NY-Alesund, Norway (78.92_N, 11.86_E) respectively; we used one year of data for a high solar activity period of 24th solar cycle, i.e. during January 2012 to December 2012.From our analysis we observed that GPS-TEC achieves its highest values during the months of October and March at low latitude, during the months of April and May at mid latitude and during September and March at high latitude while the lowest values of TEC were recorded at all the stations in December. Almost a linear relationship between ionospheric GPS-TEC with IRI-2012 and IRI-2016 was observed at low and mid latitude stations; however, high latitude TEC does not show any significant relation to IRI 2012 and IRI 2016 TEC. This research obtains a practical approach to study the ionospheric variability at low, mid, and high latitude and compares with the latest IRI-2012 and IRI-2016 models during the high solar activity period 2012.
Stellar activity effects on high energy exoplanet transits	Llama, J
Joe Llama[1], Evgenya Shkolnik[2]
[1]Lowell Observatory, [2] Arizona State Univeristy
High energy (X-ray / UV) observations of transiting exoplanets have revealed the presence of extended atmospheres around a number of systems. At such high energies, stellar radiation is absorbed high up in the planetary atmosphere, making X-ray and UV observations a potential tool for investigating the upper atmospheres of exoplanets. At these high energies, stellar activity can dramatically impact the observations. At short wavelengths, the stellar disk appears limb-brightened, and active regions appear as extended bright features that evolve on a much shorter timescale than in the optical. These features impact both the transit depth and shape, affecting our ability to measure the true planet-to-star radius ratio. In this presentation, I will show results of simulated exoplanet transit light curves using Solar data obtained in the soft X-ray and UV by the Atmospheric Imaging Assembly onboard NASA's Solar Dynamics Observatory to investigate the impact of stellar activity at these wavelengths. By using a limb-brightened transit model coupled with disk resolved Solar images in the X-ray, extreme- and far-UV I will show how both occulted and unocculted active regions can mimic an inflated planetary atmosphere by changing the depth and shape of the transit profile. I will also show how the disk-integrated Lyman-alpha Solar irradiance varies on both short and long timescales and how this variability can impact our ability to recover the true radius ratio of a transiting exoplanet. Finally, I will present techniques on how to overcome these effects to determine the true planet-to-star radius in X-ray and UV observations.
Astrospheric Space Weather as a Factor of (Exo)Planetary Habitability	Airapetian, V
Airapetian, Vladimir S.
NASA GSFC/SEEC & American Unibversity
Recent Kepler discoveries of exoplanets located around main-sequence stars have dramatically changed the landscape of exoplanetary science. Specifically, the Kepler mission has helped to detect and characterize thousands of transit candidates and hundreds of confirmed exoplanets around K-M dwarf stars and a few planets within their habitable zones (HZ). Kepler also revealed thousands of superflares on hundreds of solar-type stars, which suggests that planet hosting stars could have profound effects on the physical and chemical evolution of exoplanetary atmospheres. What do we know about the impact of space weather on our own planet? How can we apply lessons learned from the largest solar space weather events to understand how exoplanets are affected by their host stars? In this brief review, I present our team’s recent results on how current heliophysics tools can be applied for reconstruction of astrospheric space weather (ASW) from active stars (both theory & observations) and evaluation of positive and negative ASW impacts on habitable environments of rocky exoplanets. They include the ASW effects on atmospheric erosion, chemistry and surface dosages of ionizing radiation.

Session 9 - Tool market

Conveners: Barbara Thompson (GSFC), Dean Pesnell (GSFC)

New developments and applications of Helioviewer Project services	Ireland, J
Kirill Vorobyev[1], Jack Ireland[1], Rachel Connolly[2]
[1] ADNET Systems, Inc. / NASA GSFC, MD, USA [2] WGBH and PBS Learning Media, MA, USA.
The Helioviewer Project enables heliospheric data visualization, supporting data from multiple missions and instruments. It enables the visualization of petabytes of solar data from SDO and other missions, and provides tools to create downloadable media, track solar events, and access the science data behind the images. We discuss the latest changes to Helioviewer Project services, in particular the web client helioviewer.org, the provision of images from the Mauna Loa Solar Observatory, and support for the labeling of celestial bodies and the orbits of the Parker Solar Probe and the Solar Orbiter. We discuss the use of the Helioviewer Project API to develop a helioviewer.org user interface aligned with US middle and high school instructional use, available at student.helioviewer.org, created specifically for students. This client offers many of the same features of the fully fledged helioviewer.org, but is streamlined to lower the barrier to entry. This new client provides the means to access targeted observation layers which serve to highlight a subset of the available observations and events that are aligned with educational standards, making it easier to dive-in and begin the process of discovery. The new client student.helioviewer.org and associated educational resources, has been developed in conjunction with WGBH’s Bringing the Universe to America’s Classroom Project and distributed on PBS LearningMedia. We discuss the usage of this client in comparison to helioviewer.org and describe how student.helioviewer.org can drive a back-end redesign of Helioviewer Project services to take full advantage of cloud computing architectures.
sTools - a software package for data reduction of GREGOR instruments and general data analysis	Diercke, A
Christoph Kuckein[1], Carsten Denker[1], Meetu Verma[1], Horst Balthasar[1], Andrea Diercke[1,2], Sergio Javier González Manrique[3], Ekaterina Dineva[1,2], Ioannis Kontogiannis[1], Zili Shen[4,1]
[1]Leibniz-Institut für Astrophysik Potsdam (AIP), [2]Universität Potsdam, [3]Astronomical Institute, Slovak Academy of Sciences, [4]University of Texas at Austin
The optical solar physics group at AIP is responsible for the GREGOR Fabry-Perot Interferometer (GFPI) and the large-format facility cameras (Blue Imaging Channel (BIC) and High-resolution Fast Imager (HiFI)) at the 1.5-meter GREGOR solar telescope (Tenerife, Spain). Since the »Early Science Phase« of the telescope in 2014, the group developed a data reduction pipeline for these two instruments. The pipeline »sTools« is based on the Interactive Data Language (IDL) and delivers reduced and image-restored data with a minimum of user interaction. Furthermore, it creates quick-look data and builds a webpage with an overview of the observations and their statistics (http://gregor.aip.de). However, during the last years, sTools continuously evolved and currently hosts many additional routines for data analysis: (1) A local correlation tracking (LCT) algorithm adapted for both high-resolution (GREGOR and Hinode) and synoptic full-disk (SDO) data. (2) A new quantitative tool, i.e., a Background-subtracted Solar Activity Map (BaSAM), to assess and visualize the temporal variation of the photospheric magnetic field and the EUV 160 nm intensity. This method utilizes SDO data and is applicable to both full-disk observations and regions-of-interest. (3) Calibration of synoptic full-disk data from the Chromospheric Telescope (ChroTel) including extraction of Doppler velocities from He I 1083 nm filtergrams. (4) Analysis tools for sun-as-a-star spectroscopy for the Solar Disk-Integrated (SDI) telescope of the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI). sTools is licensed under a creative commons license and is freely available, after registration, at the abovementioned website.
The SDO AIA and HMI archive at MEDOC	Buchlin, E
Pablo Alingery[1], Éric Buchlin[1], Stéphane Caminade[1], Hervé Ballans[1], Frédéric Baudin[1], Susanna Parenti[1], Karine Bocchialini[1]
[1]Institut d’Astrophysique Spatiale, CNRS, Univ. Paris-Sud, Université Paris Saclay
MEDOC, created as the European data and operations center for SoHO, hosts also data from STEREO, SDO, and various other solar physics missions. The SDO archive at MEDOC represents more than 415TB of data, and covers the full length of the mission. It includes aia.lev1 data at a minimum cadence of 60s in the EUV channels (12s at specific periods of interest), and most of the 720s-cadence HMI series. It is complemented by a database of DEM maps derived from AIA. MEDOC provides a reliable, convenient, and fast (especially for European users) access to these SDO data, by a web interface and webservices. We also provide IDL and Python clients to these webservices, allowing complex queries and automated analyses on large datasets to be made.
SDO-EVE Data Download and Processing Using SunPy©	Templeman, B
Brandon Stone, Alex DeWolfe, Mike Chambliss, Dave Judd, Tim Plummer, Don Woodraska, Brian Templeman
Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado
As LASP expands its processing capabilities to other platforms and programming languages, an effort was initiated to add functionality to SunPy for the search, download and processing of EVE data. This effort extends SunPy’s Fido search and download capabilities to gather and download EVE’s level 2 and 3 data products as well as ESP’s level 1 data product. SunPy’s Timeseries module has also been modified to ease the reading, plotting and analysis of EVE data.
NASA Rocket 36.336 Extreme Ultraviolet Spectrum	Woodraska, D
Donald Woodraska[1], Michael Klapetsky[1], Francis Eparvier[1], Andrew Jones[1], Thomas Woods[1]
Laboratory for Atmospheric and Space Physics, University of Colorado
The NASA sound rocket 36.336 was successfully launched from White Sands Missile Range on June 18, 2018 near solar minimum conditions with a payload consisting of a suite of instruments measuring the solar irradiance. The payload included twin instruments to the SDO EUV Variability Experiment (EVE) Multiple EUV Grating Spectrograph (MEGS) detectors. Absolute calibration of the payload is performed using a primary irradiance standard, the NIST Synchrotron Ultraviolet Radiation Facility (SURF) in Gaithersburg, MD. The reduced solar spectrum from 6-105 nm provides the calibration to SDO-EVE and other extreme ultraviolet irradiance measurements. Determining the calibrated spectrum involves several ground and flight corrections, data analyses, data reduction, and modeling atmospheric absorption. Ground calibration includes determining several factors: the absolute calibration at SURF (responsivity), the angular pointing dependence in the field of view (FOV), higher order spectral contributions, and the temperature dependence (gain and dark). Flight data is used to determine additional information such as the wavelength scale using solar lines, a dark current correction that also removes low-frequency noise, and an algorithm to reduce the images to spectra. The radar tracking data is used in conjunction with the NRL-MSISE00 model to remove the absorption from the thermosphere/ionosphere.
The NASA Space Science Education Consortium (NSSEC)	Young, A
C. Alex Young and the NSSEC Team
NASA Goddard Space Flight Center
The NASA Space Science Education Consortium (NSSEC): Through the Eyes of NASA to the Hearts and Minds of the Nation, provides NASA science education and public outreach programs across all SMD space science discipline divisions (heliophysics, planetary science, astrophysics, astrobiology) to broad and diverse audiences throughout the United States. Central to our program is the concept of One Accessible Universe or 1 AU. Through 1 AU, we will emphasize the necessity of making NASA space science education accessible to the country, reaching diverse populations through focused communications including facilitating access and usability for people with physical disabilities. The NSSEC emphasizes cutting edge educational technology applications, high impact NASA Big Events, and data driven science education experiences, leveraging a suite of over 30 partner organizations to reach and extensively impact undergraduate education, after school programs, informal education venues, amateur astronomers, civic groups, underserved populations, and the general public. Here we present an overview of our program especially its support of solar science.
Low Latency Space Weather Products from SDO-EVE	Jones, A
Andrew Jones
University of Colorado, LASP
The S-band house-keeping link from SDO has very low latency. The SDO-EVE-ESP downlinks a very small amount of data through this housekeeping channel, and we have been able to use these products to provide a near real-time EUV line irradiances and a proxy for the GOES XRS channels. These data are publicly available as the EVE Level 0CS data and plots.